Stator structure of built-in motor

ABSTRACT

The stator of a built-in motor must be firmly and accurately mounted on the spindle head housing or the like of a machine tool. A stator core (10), i.e., a principal component of the stator is welded partially at the circumference (14) thereof, and then the circumference of the stator core (10) held by a mandrel is finished to an accurate outside diameter by grinding. The stator core (10) thus constructed is subjected to a deformation with a lapse of time after the mandrel has been removed. To solve this problem, each lamination (12) of the stator core (10) is coated with a thermosetting adhesive, to be thereby joined together, and each lamination (12) is provided with a plurality of pressed projections (22) to be joined together by weld portions (20) on the circumference of the stator core (10), or each lamination (12) is joined together by pressing a serrated bar (26) into a bore (24) thereof, without a pressed projection (22).

TECHNICAL FIELD

The present invention relates to a stator structure of a built-in motorto be incorporated into the spindle or the like of a machine tool.

BACKGROUND ART

A built-in type spindle motor for driving the spindle of a machine toolor the like has been increasingly used recently, to meet the demand forcost reductions, floor space reductions, and miniaturization. The statorof a built-in motor for such a purpose must be accurately fixed to thespindle head housing or the like of a machine tool, and a stator core isbuilt up by superposing high-permeability steel laminations and fixedlyuniting the superposed laminations by welding the circumference thereof,and then the stator core is finished to an accurate external size bygrinding.

As the laminations of the stator core are welded only in thecircumference of the stator core, however, the laminations are notfastened together in the inside portion of the stator core, and thus theinside portion of the stator core has a low rigidity but the outsideportion of the stator core has a high rigidity. Therefore, it ispossible that the stator core is deformed with a lapse of time when thestator core having such a construction and held by a mandrel is groundand is removed from the mandrel after grinding. It is also possible forthe stator core to be deformed during transportation or when subjectedto a winding process or a varnish-impregnating process.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a statorstructure having the least possibility of deformation after manufacture.

In view of the foregoing object, in a first aspect of the presentinvention, a stator of a built-in motor is built up by superposinglaminations coated with a thermosetting adhesive.

In a second aspect of the present invention, a stator of a built-inmotor is built up by superposing laminations, each provided with throughholes, and by welding the outer circumference of the laminated structureand pressing connecting bars provided with projections in thecircumferences thereof into the through holes of the laminatedstructure.

In a third aspect of the present invention, a stator of a built-in motoris built up by superposing laminations, each provided at predeterminedpositions with projections formed by pressing so as to project in onedirection, with the projections engaging the adjacent laminations toform a laminated structure, and welding the outer circumference of thelaminated structure.

The rigidity of the inside portion of any one of those stator isenhanced, as well as the outside portion of the same, by the adhesiveand the connecting bars or the projections, so that the difference inthe rigidity of the outside portion and the inside portion is small, andconsequently, the stator is less liable to be deformed. When thelaminations are coated entirely with the adhesive, in particular, thedifference in the rigidity of the outside portion and the inside portionis reduced to the smallest extent possible, and the stator has a highrigidity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a rotor core according to the presentinvention;

FIG. 2a is a sectional view of the rotor core taken along the lineII--II in FIG. 1;

FIG. 2b is an enlarged broken portion of FIG. 2a showing the coatedadhesive.

FIG. 3 is a front view of a rotor core in a second embodiment accordingto the present invention;

FIG. 4 is a fragmentary sectional view taken along the line IV--IV inFIG. 3;

FIG. 5 is a front view of a rotor core in a third embodiment accordingto the present invention; and

FIG. 6 is a fragmentary perspective view of a serrated bar.

BEST MODE OF CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings. Referring toFIGS. 1 and 2a, 2b, a stator core 10, i.e., the body of a stator for amotor, is built up by a plurality of stocked, superimposedhigh-permeability steel laminations 12. The stator core 10 is fabricatedby applying a thermosetting adhesive 11, such as an epoxy resin, to theentire surfaces of the high-permeability laminations 12 in a film havinga thickness of several microns, superposing the high-permeabilitylaminations 12 to form a laminated structure, compressing the laminatedstructure with a jig for temporary fixing, heating the laminatedstructure at a temperature of about 150° C. for a predetermined time, tojoin the high-permeability laminations 12 firmly together, and grindingthe outer circumference 14 of the laminated structure held by a mandrelto improve the accuracy of the outside diameter of the laminatedstructure. Since the component laminations 12 of the stator core 10 arecoated entirely with the adhesive 11, the stator core 10 has a uniformrigidity, and since the component laminations 12 are joined firmlytogether, the stator core 10 is not deformed and the given outsidediameter sized by grinding is maintained after the mandrel has beenremoved. Accordingly, the stator core 10 can be accurately incorporatedinto the spindle head housing (not shown) or the like of a machine tool,for example, by a shrinkage fit, so that an accurate rotative driving ofthe spindle can be effected.

The outer circumference of the stator core 10 in the first embodimentdoes not need the welding essential to the conventional stator core, buta stator core in a second embodiment according to the present inventionemploys welding in addition to the other fastening means. Referring toFIGS. 3 and 4, each component lamination 12 of a stator core 10 isprovided with pressed projections 22 at a plurality of positions (ateight positions in this embodiment). The pressed projections 22 areformed when punching out the laminations 12 from a sheet. For example,the height of the pressed projections 22 is about 1 mm when thethickness of the laminations 12 is on the order of 0.5 mm. The eightpressed projections 22 are formed in each lamination 12 between theouter circumference 14 and the inner circumference 16, at positions asnear as possible to the inner circumference 16. Since the laminations 12are provided in the inner circumferences thereof with recesses 18 forforming slots, the pressed projections 22 are formed near the recesses18. The pressed projections 22 are arranged at equal angular intervals.The weld portions 20 of the outer circumference of the stator core arepositioned at intermediate angular positions between the adjacentpressed projections 22.

This construction increases the rigidity of the inside portion of thestator core to reduce the difference in the rigidity of the outsideportion and the inside portion of the stator core, and enhances thegeneral rigidity of the stator core; that is, the pressed projectionsengage each other as shown in FIG. 4 to enhance the general rigidity ofthe stator core.

A third embodiment according to the present invention will be describedhereinafter with reference to FIGS. 5 and 6. The outer circumference 14of the stator in the third embodiment, similar to the stator shown inFIG. 3, has eight weld portions 20 distributed at equal angularintervals fusing the laminations at their periphery. Bores 24 are formedin the stator core at middle angular positions between the angularpositions of the adjacent weld portions 20. As shown in FIG. 6, serratedbars 26 externally provided with ridges 28 are pressed in the bores 24to join together the component laminations 12 of the stator core. Sincethe serrated bars 26 have longitudinally extending ridges, the bores 54are formed on a circle of a diameter greater than that of a circle onwhich the pressed projections 22 shown in FIG. 3 are arranged, but it ispreferable to form the bores 24 as near as possible to the innercircumference 16.

The stator core in the third embodiment, when compared with theconventional stator core formed by fastening together the componentlaminations by welding only the circumference 14, has a small differencein the rigidity of the outside portion and inside portion and has a highgeneral rigidity, because the component laminations are joined firmlytogether in the inside portion of the stator core with the serrated bars26.

As apparent from the foregoing description, the present inventionreduces the difference in the rigidity of the outside portion and theinside portion of a stator core and enhances the general rigidity of thestator core, and thus the possibility of deformation with a lapse oftime is significantly reduced when a mandrel is removed after grindingthe circumference of the stator core held on the mandrel. Thus, thepresent invention provides a stator finished to a high accuracy andhaving a high reliability for a built-in motor.

We claim:
 1. A stator core structure of a built-in motor comprising:aplurality of stacked superimposed laminations, each lamination having aplurality of weld portions distributed at equal angular intervals aboutan outer peripheral surface, and a plurality of axial bores formedtherein near an inner peripheral surface at angular positions betweenthe angular positions of the weld portions; said laminations of saidstator core structure being fixedly united at the stacked superimposedlaminations' outer peripheral surfaces at said weld portions; and saidcore structure being reinforced by a plurality of serrated bars havinglongitudinally extending ridges pressed, respectively, in said pluralityof axial bores formed in said stacked superimposed laminations tothereby enhance general rigidity of said core structure.